Black-surround color picture tube

ABSTRACT

The screen area of a color cathode-ray tube has a multiplicity of phosphor dot triads and the individual phosphor dots are surrounded by a deposit of graphite or other light-absorbing material. The screen has at least two surfaces functioning as diffuse light reflectors. One surface is the customary backing layer of aluminum and the other is a light-reflecting layer applied over the graphite. Multiple reflections from these surfaces permit light developed by the phosphor dots and otherwise attenuated in the graphite to be added to the useful light output of the tube.

United States Patent 1 3,614,503

[72] Inventor Leonard Dietch [56] References Cited $111,12 ,111, UNITED STATES PATENTS ii i ii i 24 1970 3,146,368 8/1964 Fioreetal 313/9213 p tented Oct-19,1971 3,365,292 1/1968 Fiore et 111.... 313/923 l a 3 3,519,868 7/1970 Schwarz 313/9213 [73] Assignee Zenith Radio Corporation Chicago, Ill. Primary Examiner-Roy Lake Y h Assistant Examiner-V. Lafranchi AttorneyFrancis W. Crotty ABSTRACT: The screen area of a color-cathode-ray tube has a multiplicity of phosphor dot triads and the individual BLACK'SURROUND COLOR PICTURE TUBE phosphor dots are surrounded by a deposit of graphite or 7 Clams 6 Drawmg other light-absorbing material. The screen has at least two sur- [52] US. Cl 313/92 CS, faces functioning as diffuse light reflectors. One surface is the 96/36.] customary backing layer of aluminum and the other is a light- [5 1] Int. Cl G03c 5/00, reflecting layer applied over the graphite. Multiple reflections HOlj 29/32 from these surfaces permit light developed by the phosphor [50] Field of Search 3l3/92 R, dots and otherwise attenuated in the graphite to be added to 92 PH, 92 CS the useful light output of the tube.

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BACKGROUND OF THE INVENTION The invention is particularly concerned with improving the light'output of a black-surround color picture tube. Such a tube has interleaved deposits of different phosphor materials and the spaces between those deposits are filled with a lightabsorbing material which is usually graphite or some other black material from whence the structure derives its name.

Thephosphor may be applied in the form of strips or dots but for the purpose of a specific disclosure particular attention will be directed to the mosaic type of screen characterized by a multiplicity of dot triads distributed over the screen area with each such triad comprising a dot of green, a dot of blue and a dot of red phosphor.

In addition to a choice as to the configuration of the phosphor deposit, tubes of the type under consideration also give a choice with respect to the relative dimensions of the phosphor dots and the electron beams. If desired, the diameter of the electron beam may be smaller than the diameter of the phosphor dot but preferably the converse relation is employed and the electron beams are made larger than the phosphor dots. Such a structure is described and claimed in US. Pat. No. 3,146,368 issued on Aug. 25, 1964 to Joseph P. Flore et al. This structure has distinct advantages over other forms of shadow mask color tubes in respect of both brightness and contrast.

If it is recognized that an excited phosphor emits light in all directions in the manner of an isotropic light source, such as a point of light source, it will be appreciated that some portion of the light generated in the black-surround tube tends to be attenuated and lost because it enters the graphite or light-absorbing material which surrounds the individual phosphor dots. If this component of the generated light can be recaptured at least in part and be redirected through the faceplate of the tube, a desirable increase in light output may be accomplished. The present invention describes new screen structures for achieving such a desired result.

Accordingly, it is an object of the invention to provide a black-surround type of color cathode-ray tube which has an enhanced light output.

It is a specific object of the invention to improve the screen structure of such a tube to recover and utilize components of light developed by the phosphor which components otherwise tend to be absorbed by the light-absorbing material surrounding the phosphor dots.

SUMMARY OF THE INVENTION The invention is an improvement in a color cathode-ray tube having a screen comprised of interleaved deposits of phosphor material which emit light of different colors and further comprised of light-absorbing material surrounding the phosphor deposits. The improvement comprises a plurality of diffusely reflecting materials superposed over the phosphor deposits and the light-absorbing material and spaced with respect to one another to simulate a multiplicity of integrating spheres surrounding the phosphor deposits.

In one specific embodiment of the invention, the phosphor deposits overlap the light-absorbing material and a diffuse light reflector is interposed between those portions of the phosphor deposits and the light-absorbing material that are in overlapping relation. The usual aluminized backing layer, which is applied over both the phosphor deposits and the lightabsorbing material, in conjunction with the first-mentioned reflector, provides the multiple reflecting surfaces relied upon to recapture and utilize light rays issuing from the phosphor dots and subject, in the absence of the multiple reflectors, to be attenuated and lost.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGS. 1 to 5 are fragmentary views pertaining to one embodiment of the invention; and

FIG. 6 is a similar view of a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The envelope of a shadow mask color tube has a face plate section that is initially separated from a conically shaped envelope portion. A fragmentary portion 10 of such a faceplate section of screen of a color cathode-ray tube is represented in FIG. 1 and may be considered as a substrate to which is applied deposits of various materials which collectively define the screen. Neither the size or configuration of the substrate is of any particular consequence, nor is it of any special moment whether the phosphor be applied by way of strips or dots. For the purpose of a specific disclosure, however, it will be assumed that faceplate 10 is part of the screen section of a 25 inch rectangular color tube having a mosaic type of screen with dot triads distributed uniformly over the internal screen surface and with each such triad comprised of a dot of green, a dot of blue and a dot of red phosphor. Since the invention con cems color tubes of the black-surround variety, the dots of all of the triads are circumscribed by light-absorbing material such as graphite, that is to say, all of the screen surface between the phosphor deposits is covered with such material. Obviously, there is a choice of developing the dot triads and then applying the surround material or, alternatively, the lightabsorbing material may be applied first and provided with discontinuities or holes into which the phosphor is subsequently deposited. There is a preference to the latter procedure and, again for the sake of a particular disclosure, the process steps for such a procedure will be described.

After the screen has been made chemically clean, it is coated with a removable layer 11 of clear polyvinyl alcohol (PVA) sensitized with ammonium dichromate. After layer II has been dried, selected portions thereof are exposed to ultraviolet light to establish in the layer interleaved sets of images of those elemental areas of the screen that are to receive assigned ones of the phosphor materials. This is accomplished in a step analogous to that conventionally taken in photoresist screening to define the elemental areas of the screen which are to receive particular phosphor and to distinguish them from the other portions of the screen. Such discrimination is easily attained by exposure to ultraviolet light through the holes or apertures of the shadow mask of the tube in process. For that purpose, the shadow mask (not shown) is installed within the faceplate section of the tube envelope in juxtaposition with respect to the internal surface of the screen and this subassembly, with the screen bearing PVA layer 1 I, is placed in an exposure chamber so that ultraviolet light is directed to selected elemental areas of the screen through the holes of the mask. If the light source has been positioned to simulate the electron gun of the tube in process which is intended to excite the green phosphor material, the ultraviolet light will be confined to expose only those portions llg of layer 11 which overlie elemental areas of screen 10 assigned to receive deposits of green phosphor. After this exposure, a similar series of portions llb of layer II are exposed, these constituting the portions of layer 11 that overlie elemental areas of the screen to receive deposits of blue phosphor. To achieve their exposure, it is only necessary to modify the position of the light source in the exposure chamber, or to place the subassembly of faceplate and shadow mask in another exposure chamber having a light source simulating the electron gun of the tube intended to energize the blue phosphor dots. In a like but third exposure step, with the light source simulating the electron gun of the tube that is to excite the red phosphor dots, a third set of portions llr of layer 11 are exposed and these portions overlie elemental areas of the screen assigned to receive red phosphor. As a consequence of the multiple exposures, there are established in layer 11 interleaved sets of images of circular, elemental areas of the screen separated from one another and intended to receive assigned ones of the phosphor materials. Between these sets of images there are portions of layer 11 that have not been exposed and these portions are represented with crosshatching in FIG. 1.

While not essential to the invention, it is preferred that the exposed elemental areas of layer 11 be smaller in size than the apertures of the shadow mask as that mask is finally and permanently installed within the completed tube. The correct relative size may be realized in a variety of ways. The mask may be provided initially with holes of a desired final size but coated or otherwise temporarily closed or reduced in size so that the dimensions of the phosphor dots, determined by exposing layer 11 through the coated shadow mask, are properly related to the final size of the mask apertures. If closing down of the mask apertures by a coating technique is resorted to, the mask coating is removed after screening has taken place so that the final hole size of the mask is properly related to the diameter of the phosphor dots. A more attractive process currently in commercial use is one in which the apertures originally formed in the mask have the precise size required for screening. In this case after screening has been completed, the mask is reetched to open up or enlarge its apertures to the desired final size. This has an advantage in precisely controlling the dimensions of the phosphor dots and also in attaining uniformity of size and configuration of the dots.

By whichever approach the selected portions 11g, 11b and llr of PVA layer 11 are exposed, the interleaved sets of images resulting from such exposures are next developed by removing all unexposed portions of photosensitive layer 11 producing the screen condition of FIG. 2. Inasmuch as the photosensitive material of layer 11 as applied to screen is soluble in water, whereas all exposed portions thereof have been rendered insoluble, washing the screen with water after the third exposure step removes all of the unexposed portions of layer 11. The screen of FIG. 2 may be described as having clear deposits or dots of PVA separated from one another by screen portions which are bare and are to receive a pigment or a material having light-absorbing capabilities.

The next step of the screening process constitutes depositing in the spaces between the elemental screen areas covered by the dots of clear PVA a coating 13 of an inorganic pigment having light-absorbing capabilities and having the property that its adherence to screen 10 is substantially immune to attack by an active agent which may be employed to destroy the adherence of PVA dots llg, 11b and llr to the screen. While this light-absorbing material may be applied only to the areas surrounding the clear PVA dots, it is more convenient to apply coating 13 over the entirety of the screen, as indicated in FIG. 3, in which case the coating of light-absorbing material is also applied over the clear PVA dots as an overcoat. Preferably, layer 13 is applied as slurry and also preferably it is a colloid having in suspension a fine pulverulant material such as black iron oxide, powdered mica, molybdenum disulfide, manganese carbonate, ceramic black or graphite. Colloidal graphite available under the trade name Aquadag" diluted to 3 percent solids with deionized water is a very acceptable material. After slurry coating 13 is applied, it is fixed to screen 10 by drying.

For reasons to be made clear hereafter, those portions of graphite layer 13 which intervene or surround the clear PVA dots are to be covered with a layer 14 of diffusely reflecting material. Reflecting material 14 may be applied only to the portions of graphite layer 13 which it is intended to cover. This may be done, for example, by electroplating if the PVA dots llg, 11b and llr are first stripped off screen 10 by means of a chemical stripper and, of course, if layer 13 is conductive which would be the case if it were a graphite material. Electroplating is feasible in this case because the areas to receive layer 14 are conductive, whereas the areas to be covered with phosphor are nonconductive and would not attract the material of layer 14 during electroplating. On the other hand it may be more convenient to apply layer 14, as by slurring or vapor deposition, over the entire screen area as illustrated in FIG. 3. It is now desirable to remove the clear PVA dots llg, llb and llr to establish the screen condition of FIG. 4.

If the material of layer 14 is readily penetrated by a chemical stripper which reacts with PVA to free or lift the clear PVA dots off screen 10, then a stripper such as 30 percent hydrogen peroxide and 70 percent water may be slurried over the screen. The excess stripping solution is poured off and the screen is then washed with a spray of deionized water, removing clear PVA dots 11g, 11b and llr and along with them the overcoats represented by the superposed portions of layers 13 and 14. As in the described case of electroplating, this is a convenient method of achieving the screen condition of FIG. 4 but if the material of layer 14 impairs the effectiveness of the chemical stripper desired to be used in removing the clear PVA dots, still another approach suggests itself. There may be applied over layer 14 a coating or layer of a positive photosensitive resist which has the property that, while normally insoluble in a solvent, usually being an alkali, it is rendered alkali soluble by exposure to actinic radiation such as ultraviolet light. After layer 14 has been covered by a positive photosensitive resist, three exposure steps are undertaken similar tothose described in the discussion of the exposure of portions 113, [lb and llr oflayer ll of FIG. 1. Washing with the solvent then removes the resist from the portions of layer 14 that overcoat clear PVA dots Ilg, 11b and llr to expose them so that by etching or through the application ofa chemical agent that attacks the material of layer 14 the portions thereof that overlies PVA dots 11g, 11b and Mr are removed. Now chemical stripping may be employed to remove the clear PVA dots. The resulting screen condition is that of FIG. 4 except that the screen will also have a layer of positive resist over the retained portions of reflecting layer 14. This is unobjectionable because such a resist bakes out during final bakeout of the screen in the finishing process steps of color picture tube manufacture as is well known. Accordingly, the remnant of the resist layer need not be considered further.

The screen in the condition of FIG. 4 has a black-surround material 13 circumscribing exposed circular elemental areas of screen 10 that are to receive deposits of phosphor materials which emit light of different colors when excited by electron bombardment. Over the black-surround there is a covering or layer of diffusely reflecting material 14 which may be any reflecting material that is compatible with the requirements of the tube, that is to say, which does not impair the operation of the tube or adversely affect its processing. It must be non phosphorescent and must be diffusely reflective. In general, one may use any white material such as titanium dioxide or magnesium oxide or any light-reflecting metal, such as aluminum, which is conventionally employed as a diffuse reflector backing the screen of a picture tube.

The various phosphor materials are now applied to screen 10 through the openings of the black-surround material I3. A number of techniques are known through which the phosphor may be applied; it is convenient to use a photosensitive PVA slurry which carries particles of a particular phosphor in suspension. In applying the green phosphor, for example, the entire inner surface of screen 10 is covered with a suitable layer of a green slurry and those portions which overlie the elemental areas llg of the screen intended to receive green phosphor are exposed and, after exposure, are developed by washing with water. In this manner deposits 11g of green phosphor are applied to the appropriate elemental areas of screen 10. As indicated in FIG. 5, it is convenient to have the phosphor deposit overlap the graphite or black-surround material 13. The size of the green phosphor dot and the extent to which it overlaps the black-surround material are easily determined by controlling the intensity of the ultraviolet light and the exposure interval through which the images of the green phosphor elements are developed. In like fashion, blue phosphor deposits 11b are made in the appropriate elemental areas 11b of screen and red phosphor deposits llr are made in the screen areas llr intended to receive red phosphor. The procedure for applying the dots, arrayed to form phosphor triads, is sufficiently well known in the art to require no further explanation.

After the phosphor has been applied, the screen is filmed and aluminized, receiving an electron permeable conductive layer of aluminum which is applied over both the phosphor deposits llg', 11b and llr as well as the graphite surround material 13. As a consequence the screen has a plurality of layers of diffusely reflecting materials superposed over its phosphor deposits and black surround and spaced with respect to one another to simulate a multiplicity of integrating spheres surrounding the phosphor deposits. More particularly, the conventional aluminized layer 15 is a first reflecting surface which overlies not only the phosphor dots but also the black-surround material 13. Layer 14, which is applied over substantially only the black-surround material 13, constitutes another reflecting surface. These reflectors face one another and make possible paths of multiple reflection in the manner of an integrating sphere.

Theoretically, an integrating light sphere is a sphere of diffusely reflecting material which has a small opening or port at one point on its surface. if an isotropic light source is positioned at the center of the sphere, all of the rays, in the theoretical case, eventually emerge from the small port and, therefore, all light produced by the internal source contributes to the light output of the sphere. The extent to which this phenomenon is achieved in the screen structure under consideration is determined by the extent to which the multiple difl'usely reflecting surfaces simulate such a sphere. For the specific embodiment under consideration most of each phosphor dot is directly deposited on the screen or substrate 10 and is backed by reflecting surface 15 so that a large portion of the light generated in this part of the phosphor dot as a consequence of electron excitation issues through the screen either directly or after reflection from surface 15. The remainder of each phosphor dot, namely that which overlaps graphite layer 13, is surrounded both top and bottom by facing reflecting surfaces 14 and i5 which permit of multiple reflection through which this portion of the phosphor dot contributes to the useful light output of the screen. More particularly, each phosphor particle may be likened to an isotropic light source and, therefore, a significant portion of the light developed in that part of the phosphor dot in the space between the facing reflectors l4 and 15 strikes either one or the other of these surfaces at such an angle as to be directed, after one or more reflections, through the part of the phosphor dot that interfaces with screen 10 and, thence, through the screen. Therefore, some light issuing from the overlapping part of the phosphor dot and which would normally be attenuated and lost in graphite layer 13 is redirected by reflection from surfaces 14 and 15 and contributes to the useful light output of the phosphor dot. The presence of reflecting surface 14, interposed between the overlapping portions of the phosphor dots and the graphite layer 13, minimizes the quantity of light lost in the graphite or light-absorbing layer 13 of the black-surround screen. The circumstances of multiple reflections from surfaces 14 and 15 recaptures much of the light directed toward layer 13 and adds it to the light output of the phosphor dot.

Reflecting surface 14 need extend only between the overlapping peripheral portions of the phosphor dots and graphite layer 13 but, as a practical matter, it is both more convenient and useful to have reflecting surface 14 coextensive with graphite layer 13 for the embodiment under consideration.

The version of the invention represented in FIG. 6 is different in that the phosphor deposits llg', 11b and llr do not overlap graphite layer l3. This figure, and also FlG. 5, represent that generally the phosphor dots have a greater depth or thickness than the graphite layer simply because the phosphor particles are very much larger or coarser than the graphite particles of layer 13. in this case, the difi'usely reflecting material 14 may be applied to fill the space between aluminized layer 15 and graphite layer 13. Accordingly, in this embodiment there are reflecting surfaces around the walls and over the top surface of each phosphor dot to redirect light and enhance the light output of the phosphor dots.

in general, the described arrangement increases reflectivity of the screen structure and light output. This may be used advantageously in permitting-a reduction of the phosphor dot size while preserving a desired level of light output. With a reduced dot size, a larger percentage of the screen is covered with light-absorbing material further to enhance the screen properties, such as contrast.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

lclaim:

1. In a color cathode-ray tube having a screen comprised of interleaved deposits of phosphor material which emit light of different colors and further comprised of light-absorbing material surrounding said phosphor deposits, the improvement which comprises a plurality of diffusely reflecting materials superposed over said phosphor deposits and said light-absorbing material and spaced with respect to one another to simulate a multiplicity of integrating spheres surrounding said phosphor deposits.

2. The improvement in accordance with claim I in which one of said reflecting materials comprises an electron permeable, conductive layer applied over both said phosphor deposits and said light-absorbing material;

and in which another of said reflecting materials is applied over substantially only said light-absorbing material.

3. The improvement in accordance with claim 2, for a color cathode-ray tube having phosphor deposits which partially overlap said light-absorbing material, and in which said other reflecting material is interposed between the overlapping portions of said phosphor deposits and said light-absorbing material.

4. The improvement in accordance with claim 2, for a color cathode-ray tube having phosphor deposits of substantially greater depth than said light-absorbing material, and-in which said other reflecting material fills the spaces between said lightabs0rbing material and the portions of said conductive layer that overlie said light-absorbing material.

5. In a color cathode-ray tube having a mosaic type of screen comprised of interspersed triads of phosphor deposits, individually includinga dot of green, a dot of blue and a dot of red phosphor, and further comprised of light-absorbing material surrounding said phosphor dots, the improvement which comprises:

a first electron permeable, conductive, and diffusely reflecting layer applied over both said phosphor dots and said light-absorbing material;

and a second diffusely reflecting layer applied over substantially only said light-absorbing material.

6. The improvement in accordance with claim 5, for a color cathode-ray tube having a mosaic screen with phosphor dots partially overlapping said light-absorbing material, and in which said second reflecting layer is interposed between the overlapping portions of said phosphor dots and said light-absorbing material.

7. The improvement in accordance with claim 5, for a color cathode-ray tube having a mosaic screen with phosphor dots of a given depth surrounded by lightabsorbing material of a much smaller depth, and in which said second reflecting layer comprises diffusely reflecting material surrounding said phosphor dots in the space between said light-absorbing material and the overlying portion of said first layer. 

1. In a color cathode-ray tube having a screen comprised of interleaved deposits of phosphor material which emit light of different colors and further comprised of light-absorbing material surrounDing said phosphor deposits, the improvement which comprises a plurality of diffusely reflecting materials superposed over said phosphor deposits and said light-absorbing material and spaced with respect to one another to simulate a multiplicity of integrating spheres surrounding said phosphor deposits.
 2. The improvement in accordance with claim 1 in which one of said reflecting materials comprises an electron permeable, conductive layer applied over both said phosphor deposits and said light-absorbing material; and in which another of said reflecting materials is applied over substantially only said light-absorbing material.
 3. The improvement in accordance with claim 2, for a color cathode-ray tube having phosphor deposits which partially overlap said light-absorbing material, and in which said other reflecting material is interposed between the overlapping portions of said phosphor deposits and said light-absorbing material.
 4. The improvement in accordance with claim 2, for a color cathode-ray tube having phosphor deposits of substantially greater depth than said light-absorbing material, and in which said other reflecting material fills the spaces between said light-absorbing material and the portions of said conductive layer that overlie said light-absorbing material.
 5. In a color cathode-ray tube having a mosaic type of screen comprised of interspersed triads of phosphor deposits, individually including a dot of green, a dot of blue and a dot of red phosphor, and further comprised of light-absorbing material surrounding said phosphor dots, the improvement which comprises: a first electron permeable, conductive, and diffusely reflecting layer applied over both said phosphor dots and said light-absorbing material; and a second diffusely reflecting layer applied over substantially only said light-absorbing material.
 6. The improvement in accordance with claim 5, for a color cathode-ray tube having a mosaic screen with phosphor dots partially overlapping said light-absorbing material, and in which said second reflecting layer is interposed between the overlapping portions of said phosphor dots and said light-absorbing material.
 7. The improvement in accordance with claim 5, for a color cathode-ray tube having a mosaic screen with phosphor dots of a given depth surrounded by light-absorbing material of a much smaller depth, and in which said second reflecting layer comprises diffusely reflecting material surrounding said phosphor dots in the space between said light-absorbing material and the overlying portion of said first layer. 